Arrangement for a piston and cylinder device

ABSTRACT

The hydraulic cylinder or shock absorber arrangement has a cylinder unit limiting an inner space in which a medium in the form of a gas or a liquid is intended to be placed. A forwardly and backwardly movable piston unit is placed such that it can slide within the space that is defined by the piston into a first chamber and a second chamber. An inlet/outlet is defined in the respective chambers of the cylinder unit for the addition to and removal of medium from the chambers together with devices which co-act in order to determine the relative position of the piston within the cylinder unit, an active first part of which is attached to the cylinder unit and arranged stretching into a recess that is arranged in the piston unit.

FIELD OF THE INVENTION

The present invention concerns an arrangement for a piston and cylinderdevice.

BACKGROUND AND SUMMARY OF THE INVENTION

Piston and cylinder devices as such are used in a number ofapplications, for example in the form of positioning and manoeuveringdevices such as drive cylinders in order to achieve manoeuveringmovements in machines, or in the form of shock absorbers in order toabsorb and dampen movements between elements that are jointed to pivotwith each other. The above-mentioned types of piston- and cylinderdevices, independently of whether they are designed to be used aspositioning and manoeuvering devices or as shock absorbers, have incommon that they display an inlet/outlet to each chamber such that themedium that is used can be added to and removed from the said chambers.However, for a shock absorber, the inlet/outlet to each chamber of thepiston- and cylinder device are connected together and designed as acommon channel or passage such that the medium can flow forwards andbackwards between the two chambers during the forward and backwardsmotion of the piston device in the cylinder. On the other hand, in thetype of piston- and cylinder device that is used as a drive cylinder orpositioning device, the inlet/outlet of each chamber are separate fromeach other and are each individually in flow-through connection with anexternal circuit that contains, among other things, devices for thecontrol of direction of some pressurized medium such as oil or air.

In the case of shock absorbers, the above-mentioned passage between thechambers is arranged in the actual piston device whereby the dampingforce that thus arises is mainly derived from the friction of the mediumin the channel. The said damping force can be regulated by varying theresistance to flow or the speed and rate of flow with which the mediumis allowed to flow forwards and backwards through the channel.

Recently, piston and cylinder devices have been developed with integralposition-sensitive elements, that is, devices that make it possible todetermine the motion of the piston device relative to the cylinder unit.The position-sensitive devices are usually connected to an externalcontrol unit, for example in the form of a computer. In the case ofshock absorbers, the computer can be provided with the information thatis required to control and regulate the damping properties orcharacteristic of the shock absorber in a way that is suitable for theapplication. For example, the damping force or characteristic of theshock absorber can be varied depending on the properties of the roadsurface, the speed, tilt, etc., or depending on parameters that arespecified in advance, that is, if the vehicle is to offer a smooth andcomfortable journey and thus offer high comfort for the travellers, orto allow more advanced and demanding driving. The computer can also besupplied with information about the speed, acceleration, etc., of thevehicle, in order to calculate an optimal damping characteristic of theshock absorber for the current driving conditions, based on theinformation that is supplied.

Shock absorbers are also known in which it is possible to measure thetemperature of the medium that is exchanged between the two chambers ofthe shock absorber. If the properties of the medium that has been chosento function in the shock absorber are previously known and theseproperties are stored in a computer, the measured temperature of themedium can be used to calculate its internal friction, or viscosity, ateach instant. By regulating, based on this information, the speed andthe rate of flow with which the medium is allowed to flow through theflow channel that exists between the two chambers of the shock absorber,the properties of the shock absorber can also be maintained essentiallyconstant, independent of the temperature of the surroundings or of theshock absorber itself.

Piston and cylinder devices that are currently known have fairlycomplicated constructions in order to allow the medium to flow into andout from the chambers, and to make it possible to control and guide themovements of the piston and cylinder device.

One intention of the invention is to achieve a piston and cylinderdevice that not only makes it possible for the medium to flow into andout from the chambers, but also allows in this part control and guidanceof the movements of the piston in the piston and cylinder device.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be described in more detail in the following withreference to the attached drawings, in which;

FIG. 1 shows a view in longitudinal cross-section through a shockabsorber equipped with an arrangement according to the invention;

FIG. 2 shows a view in longitudinal cross-section through a drivecylinder equipped with an arrangement according to the invention;

FIG. 3 shows a simplified block diagram of an electronic driving circuitthat is connected to the sensor unit; and

FIG. 4 shows a block diagram of the driving circuit shown in FIG. 3 in asomewhat modified and simplified embodiment.

DETAILED DESCRIPTION

In the drawings reference numeral 1 is used to generally denote a shockabsorber comprising a cup-shaped outer cylinder unit 2 and an innercylinder unit 3 that are able to move relative to each other in an axialtelescopic manner, and that are equipped at their free ends withfixtures 4 and 5, respectively, for mounting between two parts that moverelative to each other, the vibrations of which are to be damped, forexample the wheel axle in a vehicle body.

The inner cylinder 3 is equipped with end walls 6 and 7 and limits withrespect to its longitudinal axis a cylindrical inner space that has arotationally symmetric shape and in which is placed a damping medium,that is preferably in the form of a fluid or a liquid, and a forwardlyand backwardly mobile piston device 8 that acts in the cylinder spaceand that makes contact in a manner that prevents fluid leakage with theinner surface of the cylinder unit 3 to divide the cylinder space into afirst chamber 9 and a second chamber 10.

To one end of the piston device 8 is firmly attached one end of a pistonrod 11, the second end of which stretches out through a central opening12 in one end wall 6 of the inner cylinder unit 3 and which is sealedagainst the said opening 12 with respect to the fluid that is used. Theouter cup-shaped cylinder unit 2 is open towards the inner cylinder unit3 and is connected in a manner that resembles a collar in the region oftransition between the piston rod 11 and the fixture 4 such that thesame, during the relative motion of the said parts, surrounds that endwall 6 of the inner cylinder unit 3, from which the piston rod 11protrudes.

The figure shows the lower end wall 7, that is, the part that faces awayfrom the protruding end of the piston rod, is arranged an extendedtube-shaped element, generally denoted by 13, that lies coaxial with thecentral axis of the cylinder 3. The said tube-shaped element 13 has beengiven a circular cross-section, and is equipped at one of its ends witha ring-shaped base part 14 that is fixed by means of a screw connectioninto a recess 15 in the end wall 7 that opens into the second chamber10, and that has a second end that is placed into a recess 16 that liesalong the central axis of the piston device 6 and the piston rod 11. Asis shown in FIG. 1, the tube-shaped element 13 is positioned in a firstsection 16′ of the recess 16 in a manner that prevents fluid leakage andthat allows the sliding to be controlled, whereby a second section 16″of the recess 16 that lies after the first section, seen from the pointof view of the piston rod 11, having a larger diameter than the firstsection such that a ring-shaped space 17 is defined between the outersurface of the tube-shaped element 13 and the inner surface of thesecond section 16″ of the recess 16 when the shock absorber is placedinto a fully or partially compressed state. It should be realized, ifFIG. 1 is studied more closely, that the ring-shaped space 17 is thus inflow connection with the first chamber 9 of the cylinder unit 3 viaopenings 18 that stretch radially through the cavity wall of the pistonrod 11.

The hollow inner space of the tube-shaped element 13 forms a channel 19that runs axially, one end of which opens into the inner ring-shapedspace 17 of the piston rod 11 and the second end of which can be placedin flow connection with the second chamber 10 of the cylinder unit 3 viaa channel 20 that is equipped with valve devices 21 and that is arrangedin the second end wall 7. As is shown in FIG. 1, the channel 20 displaysan opening 20′ that serves both as inlet and outlet, and opens into thesaid first chamber 10. The valve device 21 can be of any known type thatis suitable for the purpose, and the invention provides the advantagethat it can be placed in a stationary unit of the shock absorber, thatis, in a unit that does not follow the motion of the piston. In theembodiment of the invention that is described here, the valve device 21is placed in a recess arranged in the end wall 7 and attached to it bymeans of a screw connection.

When the valve device 21 is in an open condition, as is shown in FIG. 1,the first chamber 9 and the second chamber 10 of the cylinder unit 3communicate with each other through the channel 19 that is formed by thehollow inner space of the element. The flow communication between thechambers 9, 10 is shown in FIG. 1 by arrows whereby the shock absorber1, in the example that is displayed here, moves towards the compressedcondition. During the motion of the piston device 3, fluid that ispassing through the tube-shaped element 13 can be removed either fromthe first chamber 9 to the second chamber 10, or vice versa. The devicesthat are used for controlling the valve device 21 are generally denotedby the functional block 25 in FIG. 1, and will be described in moredetail in the following. By regulating the degree of opening of thevalve device 21, it follows that the rate of flow of the flowingquantity of fluid can be controlled in a simple manner. During motion ofthe shock absorber, fluid is continually exchanged between the chambers9, 10 and thus the damping properties or characteristic of the shockabsorber 1 can also be easily varied.

According to the principles of the invention, the tube-shaped element 13forms part of a position-sensitive element, what is known as a “sensordevice”, from which information can be obtained in the form ofelectrical signals about physical quantities, which signals can be usedto guide and control the function of the shock absorber. The sensordevices comprising detection- and sensor elements that make it possible,among other things, to determine the position at any instant of thepiston device 8 or its speed within the cylinder unit 3, by theperformance of motion relative to each other.

The position-sensitive sensor- and detector elements can be of any knowntype, but it is preferable from the point of view of function if theyare of a type in which the sensing occurs without mechanical contact. Itis appropriate if the sensing elements are electrically insulated fromeach other and that the position-sensitive detection element is sodesigned that it forms a measurable reactive alternating currentresistance, or an impedance component, whereby the measurable reactiveelectrical impedance varies according to the position of the pistonelement in the cylinder. Further, the position-sensitive detection andsensor elements should be so designed that the electrical signal fromthe position-sensitive element can be led out from a stationary unit ofthe shock absorber, while the sensor element follows the motion of thepiston unit.

With reference to FIG. 1, the tube-shaped element 13 comprising aninductor that contains an electrical conductor 22 that is wound aroundan inner tube-shaped empty core in order to form a coil.

In the embodiment that is described here, the tube-shaped element 13 isformed of two tubes 23, 24 that are concentrically placed with onesurrounding the other, the inner one of which is manufactured from aferromagnetic material and the outer one of which is manufactured from anon-ferromagnetic material. In order to resist the high pressures thatmay exist inside the cylinder unit, it is appropriate if the inner tubeis manufactured from ferromagnetic steel while the second tube may bemanufactured from a paramagnetic material such as stainless steel. It isappropriate if the electrical coil 22 is electrically insulated embeddedbetween the said tubes in a suitable resin material. The axially lyinghollow space of the inner tube 23 thus forms at the same time a flowconnection between the first chamber 9 and the second chamber 10 of thecylinder unit 3. The outer tube 24 has an external surface that is sodesigned that it can be taken up into the first section 16′ of therecess 16 in the cylinder device 3 in a manner that prevents fluidleakage and that allows the sliding motion to be controlled. In order todetermine the position at each instant of the piston device 8 in thecylinder unit 3, the tube-shaped element 13 that has been arranged as aninductor collaborates with a sensor element that moves with the pistondevice 3 and the piston rod 11, which may suitably comprise the partsthemselves or may be in the form of a lining of, for example, brass oraluminum, that is set into one of the parts. It is also conceivable tocoat or plate the cavity wall of the recess 16 using known technologywith a layer of a material that has been selected based on the design ofthe inductor, for example aluminum, and that influences the outputsignal from the inductor. It should be realized that the technology toachieve measurable electrical [signals] such as an inductance from aninductor is well known, and that the technology in itself does not formany part of the invention as such.

During the vibrational movement of the shock absorber, the tube-shapedelement 13 is more or less surrounded by the parts 8, 11 that form thepiston unit, whereby a measurable impedance component can be obtainedfrom the inductor, in the form of an electrical signal, that variesdepending on the position of the piston device 8 in the cylinder unit 3.

The sensor devices described above are connected to a functional blockthat is denoted by the reference numerals 26 and 27, that concerns theelectrical circuits that are used for driving, guiding and controllingthe movement parameters of a shock absorber equipped with an arrangementaccording to the present invention, together with another functionalblock denoted by the reference FIG. 28 that contains devices formeasuring the temperature of the medium that flows through the saidshock absorber. It should be realized in this section that the mediumthat flows between the chambers 9, 10 of the shock absorber passes or isled via sensor devices and that the temperature of the medium at anyinstant can be measured, which, however, will be described in moredetail in the following.

Even if the particular embodiment of the invention that has beendescribed here has been principally shown and described applied to ashock absorber, it should be realized that the same can be applied in anessentially equivalent manner, to, for example, a hydraulic cylinder ofthe type that is shown in FIG. 2.

The arrangement according to the invention is shown in FIG. 2 applied toa hydraulic cylinder whereby the value 100 has been added to those partsdescribed above in FIG. 1 in order to make it perfectly clear that thoseparts that have been described above in FIG. 1 are essentiallyequivalent to the parts that are comprised in the said hydrauliccylinder. As FIG. 2 makes clear, the hydraulic cylinder, generallydenoted by the reference figure 101, comprising a cylinder unit 103 thattogether with the end walls 106 and 107 limits an inner ring-shapedspace in which is placed a piston unit in the form of a piston device108, dividing the space into a first chamber 109 and a second chamber110, together with a piston rod 111. One end of the piston rod 111 isattached to the piston device 108, while its second end protrudes fromthe cylinder unit 103 through an opening 112 in one end wall 106, whichit penetrates in a manner that prevents fluid leakage.

Further, the piston device 108 is in known manner so designed that itcan slide within the cylinder unit in a manner that prevents fluidleakage. As shown in the figure, the lower end wall 107 is arranged atube-shaped element, generally denoted by the reference figure 113, thatstretches coaxial with the central axis of the cylinder unit into arecess 116 that is arranged to run coaxial within the piston unit, inwhich the said tube-shaped element is placed in a manner that preventsfluid leakage and allows the sliding to be controlled into a firstsection 116′ of the depression 116. Similar to that which has beenpreviously described, the tube-shaped element 113 is equipped at one endwith a ring-shaped base part 114 that is fixed into a recess 115 in theend wall 107 by means of a screw connection.

As is shown in FIG. 2, a ring-shaped space 117 is formed between theinner surface of a second section 116″ of the recess 116 and the outersurface of the tube-shaped element 113.

The hollow space of the tube-shaped element 113 forms a channel 119 thatruns axially, one end of which through openings 118, which pass radiallythrough the wall of the piston rod 111 opens out into the saidring-shaped space 117, which in turn is placed in flow connection withthe chamber 109 through which the piston rod passes. The second end ofthe hollow space of the tube-shaped element 113 communicates through afirst channel 120 arranged in the end wall 107 with a first connectionto the cylinder, defined as an inlet and outlet opening 130. The secondchamber 110 of the cylinder unit communicates with a second connection130′ to the cylinder unit through a second channel 120′ that is arrangedin the end wall 107.

It should be realized that the piston unit that is taken up into thecylinder 101 can be manoeuvred forwards and backwards in the cylinder ifthe said connectors are connected to an outer circuit that comprisesdevices for controlling the direction of flow of a pressurized hydraulicmedium. As is shown by arrows in the figure, this medium is led into onechamber 110 while at the same time being withdrawn from the second,opposite chamber 109.

Similar to that which has been described above, the tube-shaped element113 also here forms part of a position-sensitive sensor device, thedesign of which is essentially equivalent to that described above.

The principle for the circuit 26 that is used to drive the inductor thatis attached to the tube-shaped element 13 is shown in the form offunctional blocks in FIG. 3, and as the figure makes clear, a voltagesupply, not shown in the figure, is fed with supply voltage, preferablybetween 5V and 15V, and provides in turn direct voltage to a followingstage, which, in addition to a driving stage not shown in the figure,comprising an oscillator 201 of a standard type known as the “LC type”that has a variable frequency and the chosen frequency region of whichis, naturally, controlled by the design of the inductor, but whichnormally lies in the interval from 10 kHz to 20 kHz for an inductancesignal that lies in the interval between 20 nH and 50 nH. A signal knownas a “positioning signal” is obtained from the LC oscillator, and variesdepending on the position of the piston device 8 within the cylinderunit 3. An oscillator 102 with a fixed frequency is further connected toand driven by the voltage supply, the purpose of which is to generate areference signal for the positioning signal that is obtained from the LCoscillator 201. The positioning signal from the LC oscillator 201 andthe reference signal from the oscillator 202 are fed to a mixer 203 thatconverts in a known manner the frequency of the positioning signal to alower and more practically manageable level and from which can bereceived a signal that corresponds to the position or state at anyinstant of the piston device 8 within the cylinder unit 3. Further, thepositioning and reference signals from the oscillators 201 and 202 arepassed, together with the signals from a clock 204, to a frequencydivider 205 that generates, based on these signals, a signal thatcorresponds to the speed at any instant of the piston device 8 withinthe cylinder unit 3.

When the inductor that is attached to the tube-shaped element 13 isexposed to temperature variations, the resistance of the coil 22 that ispart of the inductor changes, whereby, if these changes in resistanceare measured, information about the temperature of the medium that flowsbetween the chambers 9 and 10 in the cylinder unit 3 can be obtained,and thus also information about its viscosity. The arrangement accordingto the present invention has the advantage that the actual or realtemperature of the medium can be sensed directly in that the mediumcontinuously passes or is led through the inductive position-sensitivetube-shaped element 13. In this section, the current sensor denoted bythe reference numeral 206 that is connected in the form of a resistor inseries with the coil 22 of the inductor can be used not only to measurethe position or movements of the piston in the cylinder based on thevoltage drop experienced for alternating current across the winding, butalso to measure the temperature of the medium that flows through theshock absorber by measuring the resistance of the winding. Thistemperature measurement normally occurs by the coil 22 being equippedwith a further winding through which direct current is led, whereby thedrop in voltage across the inductor forms a signal that is directlyproportional to the temperature. As is denoted with the functional block207 in FIG. 3, this signal is used to create a temperature signal.

An embodiment of the circuit shown in FIG. 3 is shown in FIG. 4 in amore practically applicable form, where the reference FIG. 27 denotes acomputer control unit. As is shown by the functional blocks in FIG. 4,the positioning signal that is output from the LC oscillator 201 isreceived and converted by means of a counter 301 that reduces thefrequency to between 5 kHz and 10 kHz, a frequency that is practicallyuseful for the computer unit 27. The said positioning signals are passedto an electronic input/output channel, known as an “I/O unit” 302, thatreceives signals from a number of different sensors, providing, forexample, information about the speed of the vehicle, its loading, etc.The information that is fed to the I/O unit is further passed to aprogrammable computer unit, known as a “CPU unit” 303, that calculatesthe frequency of the modified positioning signal and thus the positionof the piston device 8 within the cylinder unit 3. On the basis of this,the CPU unit 303 also calculates the speed of the piston device 8 andits vibrational frequency, whereby information is received that isnecessary to be able to control and regulate the damping of thevibrational motions between, for example, a wheel and a vehicle body bymeans of the valve devices 21 of the shock absorber 1.

It is appropriate if a computer program is arranged for the CPU unit 303that is read as a sequence of instructions from a readable memory, knownas a “ROM unit” 304, that contains one or more control programs for theshock absorber 1 determined in advance. The commands between the variousunits in the computer 27 occur by means of the CPU unit 303, while theI/O unit controls the balance of information that is transferred betweenthe said CPU unit and the other components. A direct memory, known as a“RAM unit” 305, stores the data that is used by the CPU unit 303.

The CPU unit 303 processes data from the various sensors according to aprogram that has been determined in advance by, for example, initiallydetermining the desired level of damping based on given parameters andregulating the control device 25 that is attached to the valve device 21such that this level of damping is achieved. If, for example, therelative speed or the vibrational frequency between the wheel and thevehicle body deviates from a specified value, as might be the case ifthe speed of the vehicle increases, or if the driving conditions areinfluenced in a negative manner, it may be desirable immediately toincrease the damping power or the damping characteristic of the shockabsorber 1.

Since the CPU unit 303 can calculate the actual temperature of thedamping medium and thus also its viscosity based on the signals given bythe LC oscillator 201, the damping characteristic of the shock absorbercan be regulated on the basis of this to a nominal value: that is, avalue, for example, that corresponds to a temperature of around 20-25°C., at which the shock absorber has from the point of view of itsconstruction been designed to work. In this way, problems associatedwith conventional shock absorbers, namely the problem that the dampingpower tends to vary with the operating temperature due to variations inthe viscosity of the damping medium, can be essentially avoided.

The present invention, however, is not limited to that which isdescribed over and shown in the diagrams. It can be changed and modifiedin a number of different ways within the framework of the innovativeconcept specified in the following claims.

What is claimed is:
 1. An arrangement for a piston and cylinder device,comprising: a cylinder unit having an inner space defined therein, theinner space having a flowable medium disposed therein; a slidable pistonunit disposed in the inner space, the piston unit being movable in aforward and backward direction, the piston unit dividing the inner spaceinto a first chamber and a second chamber; a piston rod, connected tothe piston unit; the piston rod having a recess defined therein, thepiston rod having a first opening being in fluid communication with thefirst chamber; the cylinder unit having an end wall, the end wall havingat least a part of a cylinder channel defined therein; a hollow sensorelement disposed in the inner space and attached to the end wall, thesensor element having an axial sensor channel defined therein andextending therethrough, the sensor element being slidably associatedwith the piston unit and extending through the piston unit and into therecess of the piston rod, the sensor channel having a top end opening influid communication with the first opening and the first chamber and abottom end opening in fluid communication with one end of the cylinderchannel, the cylinder channel having an opposite end in fluidcommunication with the second chamber so that the medium is permitted toflow between the first and second chambers via the sensor channel andthe cylinder channel; a conductive member disposed in the sensorelement, the conductive member being connected to an electric unit fordetecting an inductance; and a control valve in operative engagementwith the cylinder channel for controlling the flow of fluid through thecylinder channel.
 2. The arrangement according to claim 1, wherein thesensor element comprises an electrically active detection element thatis comprised in a tube-shaped element collaborating with a sensorelement that is part of the piston unit.
 3. The arrangement according toclaim 2, wherein the sensor element is connected to position sensitivedetection devices that preferably consist of electrical circuits and acomputer unit.
 4. The arrangement according to claim 2 wherein thesensor element comprises an inductive functioning sensor device formedby an electrical conductor that has been wound into a coil form thatlies in the longitudinal direction of the tube-shaped element wherebythe piston unit forms the sensor element co-acting with, and shieldedby, the coil.
 5. The arrangement according to claim 4, wherein thepiston unit for formation of the sensor element is manufactured from aferromagnetic material or is designed as a coating of ferromagneticmaterial arranged in the recess defined in the piston rod.
 6. Thearrangement according to claim 5, wherein the tube shaped elementcontains two concentric tubes, one of which surrounds the other, betweenwhich tubes is placed the electrical conductor that has been wound intoa coil form.
 7. The arrangement according to claim 6, wherein the tubeshaped element is connected to one end wall of the cylinder unit.
 8. Thearrangement according to claim 1, wherein the first and second chambersof the cylinder unit are arranged to be in contact with each other bythe valve.
 9. The arrangement according to claim 8, wherein the valve isconnected to the cylinder channel for control and regulation of thedegree of opening of the same.
 10. The arrangement according, to claim9, wherein the valve is in operative engagement with the sensor elementand that the degree of opening of the valve is controlled and regulatedon the basis of signals and data that are received from the sensorelement.
 11. The arrangement according to claim 1 wherein thearrangement further comprises devices for measuring and registering thetemperature of the medium that functions in the cylinder unit.
 12. Thearrangement according to claim 11, wherein a temperature measuringdevice is connected to sensor element for control and regulation of thedegree of opening of the valve.
 13. The arrangement according to claim11 wherein the temperature sensing devices comprises an electricalmeasurement circuit to which an electrical conductor wound into the formof a coil is connected.